The latest high-power light-emitting diodes emit hundreds of lumens from a very small emission zone, only a few square millimeters. Although incandescent filament emits more lumens per square millimeter, their glass envelopes and spherical emission make them unsuitable for use with lenses. LEDs only have small encapsulating domes over them, and their hemispheric emission is much more amenable to being totally gathered by a lens. A characteristic common to nearly all illumination lenses of the prior art is rotational symmetry, due to the ease of mold fabrication by rotating machinery.
Round illumination patterns have been ubiquitous since the advent of the flashlight, not only because of fabrication restrictions but even more because of the large size of the source. The larger the light source the larger the luminaire must be to produce an illumination pattern with a sharply defined border. A square pattern necessarily requires a minimum degree of border sharpness, in that a corner is 41.4% farther out than an edge. Thus the initial circular pattern would need its edge to be no fuzzier than ±10% of its radius or it can't be turned into a square pattern. The laws of optics require than the luminaire aperture be much wider than the light source for any such sharpness to be attained. Thus only large specialty luminaire are commercially available to make square patterns from conventional light bulbs.
With the advent of the LED, its compactness provides a previously lacking ability to escape circular symmetry. This motivated the development of optical-theoretical means of delivering square or rectangular patterns from a circularly symmetric source. The prior art emphasizes wide-angle patterns of rectangular illumination, as in U.S. Pat. Nos. 5,924,788 and 7,674,019, both by Parkyn. In fact, the only way that preferred embodiments of the latter patent produce square beams narrower than ±45° is by discarding lateral rays beyond ±75°. This is because trying to bend light more than 30° with refraction alone results in disadvantageously thick lenses with excessive Fresnel reflectance and distortion.
When maximizing efficiency is a primary goal, a lens must completely surround the LED in order to collect all its light. Such a lens must collect the rays from the source that are nearly horizontal, and give them high deflection angles in order to send them toward the edge of a narrow-angle target. Refraction alone cannot deliver such high deflections, so that Total Internal Reflection (TIR) must be used. FIG. 1 shows some relevant prior art: U.S. Pat. No. 1,977,689 by Muller (1929) discloses the basic concept of an annular TIR prism surrounding a central refractive lens. U.S. Pat. No. 2,215,900 by Bitner (1940) discloses more complex profiles on the various surfaces. U.S. Pat. No. 2,254,961 by Harris (1941) discloses a conical top surface on the TIR prism. U.S. Pat. No. 7,083,297 by Matthews et al. (2006) discloses a conical TIR surface with a straight-line profile rather than the customary curved one. It was designed for a hemispherically emitting LED rather than a spherically emitting incandescent light bulb. Note that the LED is off-center, to form an automotive low beam, so that the profile of the central lens is an off-axis ellipse.
Other, less similar prior art is listed in the References, and like these four all are collimating, and all are circularly symmetric. What this prior art lacks is any capability of uniformly illuminating rectangular planar targets.